Hair loss, also called alopecia, can be caused by a number of factors. Most common is hair loss associated with male-pattern or female-pattern baldness. Stress can also cause hair loss, as can certain medications, certain poisons, hormone deficiency or excess, or autoimmune conditions.

Male and female-pattern baldness are normally inherited conditions. These tend to cause hair loss in men on the top of the head. The sides and back of the hair may remain in many cases. In women, female-pattern baldness tends to occur on the top of the head, with gradual thinning of the hair.

Numerous treatments may help slow hair loss in these conditions, or some turn to hair transplantation. Many simply accept the hair loss, which especially in men is quite common. In women, such hair loss is less socially acceptable. Women may turn to use of minoxidil or to hair transplantation to replace thinning hair.

Emotional stress can cause hair loss. As well, stress on the hair itself can cause gradual hair loss. Women and men who braid their hair in tight braids, or use ponytails are likely to encounter more hair loss than those who leave their hair loose. Cornrows pulling on the hair constantly frequently result in some hair loss.

A diverse number of medications are associated with hair loss. These include many common medications, such as anti-depressants, medications to treat arthritis, ACE inhibitors, anti-coagulants, beta-blockers, and medications to control cholesterol, birth control pills, and steroids. Not all people who take such medications will experience hair loss, however. They are a possible side effects of such drugs. In most cases, however, chemotherapy will always result in temporary hair loss. Usually hair grows back after chemotherapy ends.

Hormone deficiency or lack of appropriate nutrition can also cause hair loss. Women often notice some hair loss as they enter menopause. As well, women who have been recently pregnant notice some loss after pregnancy. The hair loss after pregnancy is due to falling levels of the hormone HCG. Women who enter menopause have decreasing levels of estrogen, which may result in some thinning of the hair.

Sometimes additional levels of hormones, like thyroid hormones, or estrogen and progesterone from birth control pills causes hair loss. Malnutrition is also associated with some alopecia. Occasionally hair loss may indicate poisoning. High levels of mercury and lead have been shown to cause hair loss.

In a relatively common condition, alopecia areata, hair is lost in patches. This is thought to be autoimmune based, and affects about one percent of the population. The hair follicles are treated by the body as foreign material and are actually attacked. This condition proves transient in about 80% of the people who have it. The other 20% may have bouts of hair loss and hair regrowth.

Other autoimmune conditions are also associated with hair loss, particularly lupus. It is unclear whether the lupus itself causes the hair loss, or the treatment for lupus, which is generally steroids, results in lost hair. Conditions like Hashimoto’s thyroiditis are also associated with loss of hair, but again it is unclear whether the condition itself, or the treatment with thyroid medication causes the hair loss.